Waves Flashcards
(32 cards)
Transverse waves
🔹A transverse wave is one where the particles vibrate or oscillate perpendicular to the direction of travel (and energy transfer)
🔹These waves can be polarized.
🔹Examples include: electromagnetic waves like radio waves and visible light.
Longitudinal waves
🔹A longitudinal wave is one where the particles vibrate or oscillate parallel to the direction of travel (and energy transfer)
🔹They cannot be polarized
🔹Examples include sound and ultrasound waves.
Displacement (x)
Displacement of a wave is the distance from its equilibrium position. It is a vector quantity. It can be positive or negative.
Amplitude (A)
Amplitude is the maximum displacement of a particle in the wave from its equilibrium position.
Equilibrium position
It is the rest position.
Wavelength (λ)
The wavelength of a wave is the distance between any two points on successive oscillations of the wave that are in phase. It is measured in metres.
What is a crest and a trough?
A crest is the highest point of a transverse wave and a trough is the lowest point.
Period ( T )
The period of a wave is the time taken to produce one complete oscillation or cycle of the wave.
Frequency ( f )
The frequency of a wave is the number of complete oscillations per second. It is measured in Hertz (Hz) or s<-1.
Phase difference
The phase difference tells us how much a point or a wave is in front or behind another wave.
(Extra bits)
• This can be found from the relative position of the crests or troughs of two different waves of the same frequency.
• Phase difference is measured in fractions of a wavelength, degrees or radians.
Waves in anti-phase
When the crest of one wave aligns with the trough of another, they are in antiphase.
(Two waves with a phase difference of 180° or π)
Waves in phase
When the crests or troughs are aligned, the waves are in phase.
(Phase difference of 360° or 2π)
Progressive waves
Waves that transfer energy are known as progressive waves.
Stationary waves
Waves that do not transfer energy are known as stationary waves.
What is a time-base setting?
The period of the wave can be determined from the time-base This is how many seconds each division represents, measured commonly in s div-1 or s cm-1
Wave equation
🔹The wave equation links frequency, wavelength and speed of a wave.
🔹The wave equation tells us that for a constant speed, the wavelength is indirectly proportional to the frequency.
V = f × λ
What is “c” in c=fλ?
It is the wave speed. However, c is often used to represent a specific speed ー the speed of light ( 3 x 10<8 ms<-1).
What is wave intensity?
The amount of energy passing through a unit area per unit time is the intensity of the wave.
• Therefore, the intensity is defined as power per unit area.
What is intensity proportional to?
The intensity of a progressive wave is directly proportional to its amplitude squared and frequency squared.
• Extra
This means that if the frequency or the amplitude is doubled, the intensity increases by a factor of 4 or 2<2.
What is the inverse square law?
Note the intensity is proportional to 1/r<2
• This means when the source is twice as far away, the intensity is 4 times less.
• The 1/r2 relationship is known in physics as the inverse square law.
Some examples of transverse waves:
• Water waves
• Electromagnetic waves
• Vibration on a guitar string
Some examples of longitudinal waves:
• Sound Waves
• Pushing and Pulling of a slinky
• Ultrasound waves
What is the Doppler effect or Doppler shift?
The frequency change due to the relative motion between a source of sound or light and an observer is known as the Doppler effect. (Or doppler shift)
What is the wave velocity for sound waves?
340 m/s
